PVC foam compositions

ABSTRACT

The density of rigid foamed articles made by the thermal decomposition of a blowing agent in a vinyl chloride polymer is reduced by the use of an organotin halide in combination with a mercaptocarboxylic acid ester or a sulfide of such ester or a mixture of the ester and the sulfide to activate the blowing agent.

This is a divisional of application Ser. No. 08/820,192 filed on Mar.19, 1997, now U.S. Pat. No. 5,710,188.

BACKGROUND OF THE INVENTION

This invention relates to the preparation of cellular vinyl chloridepolymers. It relates more particularly to combinations of certainorganotin compounds which are superior activators for blowing agentsemployed in the preparation of cellular vinyl chloride polymers.

One important utility for vinyl chloride resins is in the preparation ofrigid foamed articles. The articles are manufactured by known methodssuch as extrusion of a blend of the resin and additives with a suitableblowing agent and choosing the processing temperature such that it isabove the decomposition temperature of the blowing agent. The bubbles ofgas evolved by the blowing agent are entrapped within the molten resin,thereby forming a cellular structure that are commercially usefularticles such as pipe, decorative molding and structural siding.Usually, the polymer is melted at a temperature between 150° and 200° C.and it is necessary to include a stabilizer in the formulation for thepurpose of eliminating or at least minimizing the heat-induceddiscoloration of the vinyl chloride polymer which would otherwise occurat these temperatures. Also, when the decomposition temperature of theblowing agent is much above the processing temperature, activators areemployed to hasten the decomposition of the blowing agent and/or lowerthe decomposition temperature. The combination of a blowing agent and anactivator increases both the degree and the rate of blowing agentdecomposition. The resultant larger volume of gas generated isdesirable, since it reduces the amount of blowing agent required.

It is a well known fact that a variety of organotin compounds,particularly dimethyltin derivatives of mercaptocarboxylic acid esters,will impart useful levels of heat stability to vinyl chloride polymers.German Pat. Nos. 2,133,372 and 2,047,969 disclose the use of organotinmercaptocarboxylic acid estets in foamed polyvinyl chloride. Thesecompounds stabilize well but do not effectively activate blowing agentssuch as azobisformamide. Organotin carboxylates such as dibutyltinmaleate, dibutyltin dilaurate and dibutyltin maleate-half esters aredisclosed in Japanese Pat. No. 6264/67 as being useful in flexible,i.e., plasticized, polymer foams. Although these organotin compoundsactivate azodicarbonamides, they are poor thermal stabilizers for thepolymer. Thus, it can be seen that organotin mercaptocarboxylic acidesters impart good thermal stability but poor blowing agent activation,while organotin carboxylates offer good activation, but poor thermalstability with a resultant lack of proper melt viscosity control.

Dworkin et al teaches in U.S. Pat. No. 3,953,385 that organotincarboxylates provide only marginal improvement in the activation of ablowing agent when combined with the organotin mercaptocarboxylic acidesters described therein. In contrast to that teaching, we have foundthat organotin chlorides, in combination with organotinmercaptocarboxylic acid esters and with sulfides of such esters, areunexpectedly good activators for blowing agents such as theazobiscarbonamides, 5-phenyl tetrazole, and benzene sulfonylhydrazide infoamed polyvinyl chloride. The combination works well as a stabilizerfor the vinyl chloride polymers.

SUMMARY OF THE INVENTION

It is an object of this invention to provide more effective activatorsfor the blowing agents in the preparation of foamed vinyl chloridepolymers.

It is another object of this invention to provide a method for reducingthe density of foamed vinyl chloride polymers while also reducing theamount of blowing agent.

It is a further object of this invention to provide foamed poly(vinylchloride) articles having reduced density and containing reduced amountsof the blowing agent by-products and the blowing agent activator.

These and other objects which will become apparent from the followingdescription of the invention are achieved by a composition comprising:

a vinyl chloride polymer, a blowing agent, an organotin halide havingthe formula:

    R.sub.(4-x) SnX.sub.x                                      I

wherein R is an alkyl or cycloalkyl group having from 1 to 30 carbonatoms, X is a halogen of atomic weight 35 to 127, and x is from 1 to 3;and

at least one stabilizer selected from the group consisting of:

(A) an organotin mercaptide of a mercaptocarboxylic acid ester havingthe formula:

    R.sup.1.sub.(4-y) Sn SZ(COOR.sup.2).sub.m !y               II

wherein R¹ is an alkyl or cycloalkyl group having from 1 to 30 carbonatoms, Z is a Alkylene radical having from 1 to 30 carbon atoms, R² isan organic group derived from an alcohol having from 1 to 4 hydroxylgroups and from 1 to 30 carbon atoms, m is an integer from 1 to 4, and yis any number from 1 to 3; with the proviso that when y is less than 3,the R¹ groups may be the same or different, and when m is more than 1,the R² groups may be the same or different, and

(B) a sulfide of an organotin mercaptide of Formula II.

The sulfide may be made by mixing an alkaline aqueous solution, amercaptocarboxylic acid ester of Formula II, an alkali metal-, analkaline earth metal-, or ammonium sulfide, and an organotin chloridehaving the formula:

    R.sup.3.sub.(4-z) SnCl.sub.z                               III

wherein R³ is an alkyl or cycloalkyl group having from 1 to 30 carbonatoms, and z is any number from 1 to 3.

Alternatively, the sulfide may be made by mixing a monoalkyl- ordialkyltin sulfide with an organotin mercaptide of Formula II, and byother procedures well known in the stabilizer art. The sulfide isbelieved to include bis monoorganotin)-bis(mercaptocarboxylate)!monosulfides and polysulfides, bis(diorganotin)-mono(mercaptocarboxylate)!monosulfides and polysulfides,and products which arise during equilibrium reactions among said mono-and polysulfides, including monoalkyltin tris(mercaptocarboxylates),dialkyltin bis(mercaptocarboxylates), and oligomeric mono- anddi-organotin mono- and polysulfides. The sulfide may be describedfurther by the formula: ##STR1## wherein R⁴ is a hydrocarbyl radical; R⁵is a hydrocarbyl radical or -S-Z- C(═O)OR⁶ !; Z¹ is Alkylene radicalhaving from 1 to 30 carbon atoms; R⁶ is hydrogen, a hydrocarbyl radical,a hydroxyhydrocarbyl radical, or R⁷ --OC(═O)R⁸, wherein R⁷ is (CH₂)_(k),phenylene, or --CH═CH--, and R⁸ is a hydrocarbyl radical; n is aninteger from 1 to 3, p is from 1 to 2, q is from 1 to 10, k is 0 or aninteger from 1 to 8, and the valency of Z¹ is n+1; with the proviso thatit includes products arising from an equilibrium among the --SnR⁴,--SnR⁵, and --Sn--S--Z¹ -- C(═O)OR⁶ ! _(n) moieties, as recited above.

DETAILED DESCRIPTION OF THE INVENTION

The vinyl chloride polymers are made from monomers consisting of vinylchloride alone or a mixture of monomers comprising, preferably, at leastabout 70% by weight based on the total monomer weight of vinyl chloride.They are exemplified by copolymers of vinyl chloride with from about 1to about 30% of a copolymerizable ethylenically unsaturated materialsuch as vinyl acetate, vinyl butyrate, vinyl benzoate, vinylidenechloride, diethyl fumarate, diethyl maleate, other alkyl fumarates andmaleates, vinyl propionate, methyl acrylate, 2-ethylhexyl acrylate,butyl acrylate and other alkyl acrylates, methyl methacrylate, ethylmethacrylate, butyl methacrylate and other alkyl methacrylates, methylalpha-chloroacrylate, styrene, trichloroethylene, vinyl ethers such asvinyl ethyl ether, vinyl chloroethyl ether and vinyl phenyl ether, vinylketones such as vinyl methyl ketone and vinyl phenyl ketone,1-fluoro-2-chloroethylene, acrylonitrile, chloroacrylonitrile,allylidene diacetate and chloroallylidene diacetate. Typical copolymersinclude vinyl chloride-vinyl acetate (96:4 sold commercially as VYNW),vinyl chloride-vinyl acetate (87:13), vinyl chloride-vinylacetate-maleic anhydride (86:13:1), vinyl chloride-vinylidene chloride(95:5); vinyl chloride-diethyl fumarate (95:5), and vinyl chloride2-ethylhexyl acrylate (80:20).

The vinyl chloride polymers, of course, constitute the major portion ofthe compositions of this invention. Thus, they amount to from about 70%to about 95% by weight of the total weight of the unfoamed compositionsof this invention.

The blowing agent may be any one or a mixture of those commonly used forfoaming PVC pipe, including azobisformamide, 5-phenyl tetrazole, benzenesulfonyl hydrazide, the formula for the azobisformamide is: ##STR2##Azobisformamide is available under the CELOGEN AZRV trademark. Theconcentration of said blowing agent is suitably from about 0.1 and 5.0%but preferably from about 0.2 to about 3% by weight of the totalcomposition prior to the formation of foam.

In the organotin halide of Formula I, R is exemplified by methyl, ethyl,propyl, isopropyl, n-butyl, isobutyl, tert-butyl, amyl, hexyl, octyl,isononyl, monyl, decyl, undecyl 2-ethylhexyl, iso-octyl, lauryl,palmityl, stearyl, myristyl, behenyl, cyclobutyl, cyclohexyl, methylcyclohexyl and cyclopentyl. Hal is preferably chlorine. The organotinhalides are exemplified by butyltin trichloride, dimethyltin dichloride,trioctyltin chloride, dioctyltin dichloride, dibutyltin dibromide,dibenzyltin dichloride, dibutyltin dichloride, dioctyltin dichloride,and monooctyltin trichloride. The organo radical preferably has from 1to 8 carbon atoms and the methyl, butyl, and octyl tin groups areparticularly preferred. The organotin chloride may comprise a mixturewherein x is from 2 to 3. The organotin halides may be prepared bymethods well known in the art such as those disclosed in U.S. Pat. Nos.3,745,183, 3,857,868, and 4,134,878.

The proportion of organotin halide in the unfoamed compositions of thisinvention is from about 5 to about 15% of the weight of the heatstabilizer used in the vinyl chloride polymer composition of thisinvention.

In the organotin mercaptide of Formula II, R¹ may be, for example,methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tert-butyl, amyl,hexyl, octyl, isononyl, monyl, decyl, undecyl 2-ethylhexyl, iso-octyl,lauryl, palmityl, stearyl, myristyl, behenyl, cyclobutyl, cyclohexyl,methyl cyclohexyl and cyclopentyl. It preferably has from 1 to 8 carbonatoms, however, and the methyl, butyl, and octyl groups are particularlypreferred. Octyl is defined to include 2-ethylhexyl as well as n-octyland iso-octyl. Butyl is defined to include n-butyl, isobutyl, sec-butyl,and tert-butyl.

The Z group has from one to about thirty carbon atoms, such as analkylene, arylene or cycloalkylene radical, and in addition may containhalogen, free carboxylic acid groups, keto groups, mercapto groups,carboxylic acid salt groups, ether groups and hydroxyl groups. It ispreferred that Z is an alkylene group having from about 1 to about 8carbon atoms.

R² is an organic group derived from a monohydric or polyhydric alcoholof the formula R' (OH)_(j) where j is an integer from one to about four,but is preferably one or two. Thus, R' can be alkyl, alkylene,alkylenyl, aryl, arylene, alkaryl, aralkyl, cycloaliphatic andheterocyclic and may contain from about one to about thirty carbonatoms, and may also contain ester groups, alkoxy groups, hydroxylgroups, halogen atoms and other inert substituents. Preferably, R' isderived from a monohydric alcohol containing from one to about thirtycarbon atoms, more preferably from eight to about twenty carbon atoms,and is exemplified by methyl, ethyl, propyl, n-butyl, t-butyl, isobutyl,octyl, isooctyl, 2-ethylhexyl, decyl, lauryl, octadecyl, myristyl,palmityl, oleyl, dodecyl, and ricinoleyl alcohols, cyclic monohydricalcohols, such as cyclopropanol, 2,2-dimethyl-1-cyclopropanol,cyclobutanol, 2-phenyl-1 -cyclobutanol, cyclopentanol, cyclopentenol,cyclohexanol, cyclohexenol, 2-methyl-, 3-methyl-, and4-methyl-cyclohexanol, 2-phenyl-cyclohexanol, 3,3,5-trimethylcyclohexanol, 1,4-cyclohexadiene-3-d, cycloheptanol, cycloheptene-3-d,1,5-cycloheptadiene-3-ol, 2-methyl-, 3-methyl- and 4-methylcycloheptanol, cyclooctanol, cyclooctenol, cyclonomanol, cyclodecanol,cyclodecene-3-ol, cyclododecanol, the paramenthanols, such as3-hydroxy-p-menthane, 2-hydroxy-p-menthane, the para-menthenols such asα-terpineol, borneol, pine oil, fenchol,2,2-di-methyl-3,6-endo-methylene cyclohexanol, methyl borneol,2,2-10-trimethyl-3,6-endomethylene cyclohexanol, the cyclicsesquiterphenols such as farnesol and nerolidol, the sterols such ascholesterol, dihydrocholesterol, ergosterol, 24-ethyl cholesterol, thecondensed alicyclic alcohols such as 1-, and 2-hydroxyl-1,2,3,4-tetrahydronaphthalene and 1-, and 2-hydroxydecahydronaphthalene,or from a dihydric alcohol such as glycols containing from two to aboutthirty carbon atoms, including ehtylene glycol, propylene glycol,diethylene glycol, dipropylene glycol, tetramethylene glycol, neopentylglycol and decamethylene glycol, 2',2'-4-trimethyl pentane-diol,2,2',4,4'-tetramethyl cyclobutane-diol, cyclohexane-1,4-dimethylanol,4,4'-isopropylidene-dicyclohexanol, and polyols such as glycerine,triethylol propane, mannitol, sorbitol, erythritol, dipentaerythritol,pentaerythritol, and trimethylol propane.

The dimethyltin-, dibutyltin-, and dioctyltin- mercaptides ofbis(octylthioglycolate) are particularly suitable for the purposes ofthis invention. Also, preferred are mixtures of mercaptides wherein fromabout 80 to about 85% of the total weight of the mixture are mercaptidesin which y is about 2.

As further description of the chloride of Formula III, R³ may be, forexample, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl,tert-butyl, amyl, hexyl, octyl, isononyl, monyl, decyl, undecyl2-ethylhexyl, iso-octyl, lauryl, palmityl, stearyl, myristyl, behenyl,cyclobutyl, cyclohexyl, methyl cyclohexyl and cyclopentyl. It preferablyhas from 1 to 8 carbon atoms, however, and the methyl, butyl, and octylgroups are particularly preferred. Octyl is defined to include2-ethylhexyl as well as n-octyl and iso-octyl. Butyl is defined toinclude n-butyl, isobutyl, sec-butyl, and tert-butyl.

In Formula IV for the sulfide, R⁴ and R⁵ are preferably alkyl groupshaving from 1 to 8 carbon atoms but more preferably 1 carbon atom, R⁶ ispreferably an alkyl or cycloalkyl radical having from 1 to 17 carbonatoms, n is preferably 1, and q is preferably from 1 to 4 and morepreferably from 1 to 2. R⁶ may be, for example, methyl, ethyl, propyl,isopropyl, n-butyl, isobutyl, tert-butyl, amyl, hexyl, octyl, isononyl,monyl, decyl, undecyl 2-ethylhexyl, iso-octyl, lauryl, palmityl,stearyl, myristyl, behenyl, cyclobutyl, cyclohexyl, methyl cyclohexyland cyclopentyl.

The Z¹ group may be, for example, an alkylene, arylene or cycloalkyleneradical, and in addition may contain halogen, free carboxylic acidgroups, keto groups, mercapto groups, carboxylic acid salt groups, ethergroups and hydroxyl groups. It is preferably an alkylene group havingfrom about 1 to about 8 carbon atoms.

The S--Z--(COOR²)_(m) and S--Z¹ -- (C═O)OR⁶ !_(n) groups are derivedfrom mono- or polymercapto carboxylic acid esters by removal of thehydrogen atom of the mercapto group. These include the esters ofaliphatic, aromatic, cycloaliphatic and heterocyclic acids which containat least one mercapto group, and can also contain inert substituentssuch as halogen, hydroxyl, keto and alkoxy groups, such as, for example,esters of mercaptoacetic acid, α-mercaptopropionic acid,β-mercaptopropionic acid, mercaptooleic acid, mercaptoricinoleic acid,mercaptolinoleic acid, mercaptostearic acid, mercaptovaleric acid,mercaptohexanoic acid, mercaptooctanoic acid, thiolactic acid,mercaptolevulinic acid, mercaptolauric acid, mercaptobehenic acid,dithiotartaric acid, mercaptopalmitic acid, mercaptobenzoic acid,mercaptomethylbenzoic acid, mercaptocyclohexane carboxylic acid,3-mercapto-2,3-dimethyl butyric acid, 2-mercaptobutyric acid,3-mercaptobutyric acid, 3-mercapto-4-hydroxy butyric acid,2-mercapto-3-methylbutyric acid, 3-mercapto-4,5-dimethylhexanoic acid,3-mercaptohexanoic acid, 2-mercapto-6-hydroxyhexanoic acid,3-mercapto-4-ethylhexanoic acid, thiomalic acid, thiocitric acid,3-mercaptoglutaric acid, 2-mercaptosuberic acid, thiosalicyclic acid,2-mercaptocyclohexane carboxylic acid, 3-mercapto-2-naphthoic acid,3-mercaptofuroic acid, 2-mercaptolauric acid, thiomalic acid,mercaptoglutaric acid, mercaptoazelaic acid, mercaptomalonic acid,mercaptoadipic acid, mercaptopimelic acid, mercaptosuberic acid,mercaptosebacic acid, mercaptoterephthalic acid, and mixtures of these.

The organotin mercaptides of mercaptocarboxylic acid esters can beprepared readily by the reaction of the mercaptocarboxylic acid esterswith the corresponding organotin oxides or chlorides. For a morecomplete explanation of the process for making, and for additionalexamples of these dis-organotin mercapto esters compounds, see U.S. Pat.Nos. 2,648,650 to Weinberg et al., 2,641,596 and 2,752,325 to Leistner,and 3,115,509 to Mack, and Canadian Patent No. 649,989 to Mack.

The organotin mercapto acid esters containing two different mercaptoacid ester groups can be prepared by reacting the desired organotinoxide or chloride with a mixture of the mercapto acid esters, or byheating the two different organotin esters together.

The sulfides may be prepared by mixing an alkaline aqueous solution, amercaptocarboxylic acid ester of Formula II, an alkali metal-, analkaline earth metal-, or ammonium sulfide, and an organotin chlorideaccording to any of several well known methods such as those taught byKauder in U.S. Pat. No. 3,565,930 and Brecker in U.S. Pat. No.3,565,931, both of which are incorporated herein by reference.

Examples of the chloride that may be used include methyltin trichloride,ethyltin trichloride, butyltin trichloride, sec. butyltin trichloride,octyltin trichloride, benzyltin trichloride, dimethyltin dichloride,dipropyltin dichloride, butyl methyl tin dichloride, dibutyltindichloride, dioctyltin dichloride, dibenzyltin dichloride, phenyltintrichloride, p-tolyltin trichloride, diphenyltin dichloride,di-p-tolyltin dichloride, cyclohexyltin trichloride, dicyclohexyltindichloride, cyclopentyltin trichloride, oleyltin trichloride, dioleyltindichloride, vinyltin trichloride, diallyltin dichloride, allyltintrichloride, eicosanyltin trichloride.

The stabilizer components of the invention, including the organotinmercapto acid esters and the sulfides of organotin mercapto acid esters,are employed in an amount sufficient to impart the desired resistance toheat deterioration at working temperatures of 350° F. and above. Themore rigorous the conditions to which the resin will be subjected duringworking and mixing, and the longer the term required for resistingdegradation, the greater will be the amount of organotin mercapto acidester required. Generally, as little as 0.25% total of the stabilizercomponents by weight of the resin, will give resistance to heatdeterioration. They may be incorporated into the compositions byadmixing in an appropriate mill or mixer or by any of the other wellknown methods which provide for the uniform distribution of thestabilizers throughout the composition. The preparation of the polyvinylchloride resin composition is easily accomplished by conventionalprocedures. For example, the selected stabilizer combination may beformed as above, and then blended with the polyvinyl chloride resin on atwo or three roll mill at a temperature at which the mix is fluid andthorough blending facilitated, e.g., at from 250 to 375° F., for a timesufficient to form a homogeneous mass. After the mass is uniform, it issheeted off in the usual way.

There is no critical upper limit on the amount, but amounts above about10% by weight of the resin do not give an increase in stabilizingeffectiveness commensurate with the additional stabilizer employed.Preferably, the amount is from about 0.5 to about 5% by weight of theresin.

The stabilizer combination of the invention can be employed togetherwith other polyvinyl chloride resin stabilizers. The stabilizercombination of the invention in this event will be the major stabilizer,and the additional stabilizer will supplement the stabilizing action ofthe former, the amount of the stabilizer combination being within therange from about 0.25 to about 15 parts by weight per 100 parts of theresin, and the additional stabilizer being in an amount of from about0.05 to about 10 parts per 100 parts of the resin.

Among the additional metallic stabilizers are included other organotincompounds, polyvalent metal salts of medium and or high molecular weightfatty acids and phenols, with metal such as calcium, tin cadmium,barium, zinc, magnesium and strontium.

In addition to the blowing agent activator-heat stabilizer compositionsdescribed in the foregoing specification and appended claims, the vinylchloride polymer compositions of this invention may contain additivesfor the purpose of increasing, resistance to oxidation, flame retardancyand impact resistance of the polymer. Pigments, fillers, dyes,ultraviolet light absorbing agents and the like may also be present.Conventional processing aids such as lubricants and acrylic resins canalso be present.

Acrylic resins are employed in the compositions of this invention asprocessing aids to improve melt elasticity and strength and to preventthe collapse of the cellular structure during processing. The amount ofthe acrylic resin is from about 2 to about 15 parts per hundred parts ofthe vinyl chloride polymer. The molecular weight of the resin may be inthe range of from 300,000 to 1,500,000 but those having the highermolecular weights are preferred; resins having a molecular weight of1,000,000 and higher are particularly preferred. Examples of the acrylicprocessing aids include those sold by Rohm & Haas under the trademarkACRYLOID and product numbers K-175, and K-400.

A small amount, usually not more than 1.5%, of a parting agent orlubricant, also can be included. Typical parting agents are the higheraliphatic acids, and salts having twelve to twenty-four carbon atoms,such as stearic acid, lauric acid, palmitic acid and myristic acid,lithium stearate and calcium palmitate, mineral lubricating oils,polyvinyl stearate, polyethylene and paraffin wax.

Impact modifiers, for improving the toughness or impact-resistance ofunplasticized resins, can also be added to the resin compositionsstabilized by the present invention in minor amounts of usually not morethan 10%. Examples of such impact modifiers include chlorinatedpolyethylene, ABS polymers, and polyacrylate-butadiene graft copolymers.

Among the antioxidants suitable for use in the present polymercompositions are phenols, particularly those wherein the positionsadjacent to the carbon atom bearing the hydroxyl radical contain alkylradicals as substituents. Phenols wherein this alkyl radical issterically bulky, e.g. a tertiary butyl radical, are preferred.

A small amount, usually not more than 0.1%, of a metal release agent,such as an oxidized polyethylene, also can be included.

The effect of the blowing agent activator is independent of whether itis added to the vinyl chloride polymer as an aqueous solution, as partof a stabilizer package, or as part of a lubricant package. A variety ofconventional molding and extruding techniques may be used to form therigid, cellular vinyl chloride polymers of this invention into pipe orany desired profile or a sheet.

The following examples illustrate this invention more specifically.Unless otherwise indicated, all parts and percentages in these examplesand throughout this specification are by weight. ABF is an abbreviationof azobisformamide.

EXAMPLE 1 & COMPARATIVE EXAMPLE 1

PVC pipe formulations A and B were processed in a Brabender 3/4 inchextruder having a 25/1 length to diameter ratio and a straight flightscrew having a 2/1 compression ratio and a die orifice of 5 mm. Thetemperature profile (° C.) was:

Zone 1 155 Zone 2 158 Zone 3 170 Die 170.

The formulations for the product of Example 1 and for the ComparativeExample are the same except for the addition of the monomethyltintrichloride in Example 1 as shown in the following table. The extrusionresults are also given in the table.

                  TABLE 1    ______________________________________                  Comp. Ex. 1                          Example 1    ______________________________________    FORMULATION    PVC             100       100    Acrylic resin    K-400           6         6    K-175           6         6    CaCO.sub.3      5         5    TiO.sub.2       1         1    Ca stearate     1.2       1.2    AC-629*         0.08      0.08    Paraffin wax    0.75      0.75    Azobisformamide 0.35      0.35    Monomethyltin   0.00      0.10    trichloride    Extrusion Results    RPM             60        60    Torque m. gm.   5300      5100    Melt temp. (orifice)                    192       192    Output gm/min   68.2      67.6    Foam Density gm/cc                    0.58      0.54    ______________________________________    *trademark for oxidized polyethylene

EXAMPLE 2, AND COMP EXAMPLE 2

The rate of gas evolution during the decomposition of the blowing agentin the presence a stabilizer was measured by immersing a test tubefitted with a means for trapping the evolved gas and containing 1 gramof blowingagent and 10 grams of stabilizer in an oil bath maintained at200° C. The volume of gas was recorded at 1 minute intervals for thefirst fiveminutes and then at five minute intervals for the next 25minutes. The stabilizer in Comparative Example 2 was dimethyltinbis(di-ethylhexyl thioglycolate) and in Example 2 it was dimethyltinbis(di-ethylhexyl thioglycolate) plus 10% of monomethyltin trichlorideby weight of the thioglycolate. The data is given in Table 2.

                  TABLE 2    ______________________________________                 Milliliters of Gas Evolved    TIME, minutes  Ex. 2     CE 2    ______________________________________    1              7          0    2              15         5    3              87         20    4              102        77    5              107        82    10             122        90    15             132        95    20             142       102    25             155        110.    ______________________________________

The subject matter claimed is:
 1. A composition comprising a vinylchloride polymer, a blowing agent, an organotin halide having theformula:

    R.sub.(4-x) SnX.sub.x                                      I

wherein R is an alkyl radical having from 1 to 18 carbon atoms, and X ishalogen of atomic weight 35 to 127, and x is from 1 to 3; and at leastone stabilizer selected from the group consisting of:(A) an organotinmercaptide of a mercaptocarboxylic acid ester having the formula;

    R.sup.1.sub.(4-y) Sn SZ(COOR.sup.2).sub.m !Y               II

wherein R¹ is an alkyl or cycloalkyl group having from 1 to 30 carbonatoms, Z is an alkylene radical having from 1 to 30 carbon atoms, R² isan organic group derived from an alcohol having from 1 to 4 hydroxylgroups and from 1 to 30 carbon atoms, m is 1, and y is any number from 1to 3; with the proviso that when y is less than 3, the R¹ groups may bethe same or different, and (B) a sulfide of an organotin mercaptide ofFormula II ##STR3##
 2. The composition of claim 1 wherein Z is analkylene radical.
 3. The composition of claim 1 wherein mercaptides inwhich y is about 2 are from about 80 to about 85% of the total weight ofthe mercaptides.
 4. The composition of claim 2 wherein R is an alkylgroup having from 1 to 8 carbon atoms.
 5. The composition of claim 1wherein the sulfide has the formula: ##STR4## wherein R⁴ is ahydrocarbyl radical; R⁵ is a hydrocarbyl radical or --S--Z-- C(═O)OR⁶ !;Z¹ is an alkylene radical having from 1 to 30 carbon atoms; R⁶ ishydrogen, a hydrocarbyl radical, a hydroxyhydrocarbyl radical, or R⁷--OC(═O)R⁸, wherein R⁷ is (CH₂)_(k), phenylene, or --CH=CH--, and R⁸ isa hydrocarbyl radical; n is 1, p is from 1 to 2, q is from 1 to 10, k is0 or an integer from 1 to 8; with the proviso that it includes productsarising from an equilibrium among the --SnR⁴, --SnR⁵, and --Sn--S--Z¹ --C(═O)OR⁶ ! moieties.
 6. The composition of claim 1 wherein R² is anorganic group derived from a monohydric alcohol having from 8 to 20carbon atoms.
 7. The composition of claim 2 wherein R² is an organicgroup derived from a monohydric alcohol having from 8 to 20 carbonatoms.
 8. The composition of claim 5 wherein R² is an organic groupderived from a monohydric alcohol having from 8 to 20 carbon atoms. 9.The composition of claim 8 wherein Z¹ is an alkylene radical.